The Foundations of Chemistry

Exercises 227

Exercises

Particles and the Nuclear Atom

*001.List the three fundamental particles of matter, and indi-

cate the mass and charge associated with each.

*002.(a) How do we know that canal rays have charges oppo-

site in sign to cathode rays? What are canal rays? (b) Why

are cathode rays from all samples of gases identical,

whereas canal rays are not?

00 *3.The following data are measurements of the charges on

oil droplets using an apparatus similar to that used by Mil-

likan:

13.458 10 
^19 C 17.308 10 
^19 C

15.373 10 
^19 C 28.844 10 
^19 C

17.303 10 
^19 C 11.545 10 
^19 C

15.378 10 
^19 C 19.214 10 
^19 C

Each should be a whole-number ratio of some funda-

mental charge. Using these data, determine the value of

the fundamental charge.

00 *4.Suppose we discover a new positively charged particle,

which we call the “whizatron.” We want to determine its

charge.

(a) What modifications would we have to make to the

Millikan oil-drop apparatus to carry out the corre-

sponding experiment on whizatrons?

(b) In such an experiment, we observe the following

charges on five different droplets:

5.76 10 
^19 C 7.20 10 
^19 C

2.88 10 
^19 C 10.08 10 
^19 C

8.64 10 
^19 C

What is the charge on the whizatron?

*005.Outline Rutherford’s contribution to understanding the

nature of atoms.

*006.Why was Rutherford so surprised that some of the

-particles were scattered backward in the gold foil

experiment?

*007.Summarize Moseley’s contribution to our knowledge of

the structure of atoms.

*008.The approximate radius of a hydrogen atom is 0.0529 nm,

and that of a proton is 1.5 10 
^15 m. Assuming both the

hydrogen atom and the proton to be spherical, calculate

the fraction of the space in an atom of hydrogen that is

occupied by the nucleus. V(4/3) r^3 for a sphere.

*009.The approximate radius of a neutron is 1.5 10 
^15 m,

and the mass is 1.675 10 
^27 kg. Calculate the density

of a neutron. V(4/3) r^3 for a sphere.

Atom Composition, Isotopes, and Atomic Weights

*010.Arrange the following in order of increasing ratio of

charge to mass:^12 C,^12 C^2 ,^14 N,^14 N^2 .

*011.Refer to Exercise 10. Suppose all of these high-energy

ions are present in a mass spectrometer. For which one

will its path be changed (a) the most and (b) the least by

increasing the external magnetic field?

*012.Estimate the percentage of the total mass of a^6529 Cu atom

that is due to (a) electrons, (b) protons, and (c) neutrons

by assumingthat the mass of the atom is simply the sum

of the masses of the appropriate numbers of subatomic

particles.

*013.(a) How are isotopic abundances determined experimen-

tally? (b) How do the isotopes of a given element differ?

*014.Define and illustrate the following terms clearly and con-

cisely: (a) atomic number, (b) isotope, (c) mass number,

(d) nuclear charge.

*015.Write the composition of one atom of each of the three

isotopes of silicon:^28 Si,^29 Si,^30 Si.

*016.Write the composition of one atom of each of the four

isotopes of sulfur:^32 S,^33 S,^34 S,^36 S.

*017.Complete Chart A for neutral atoms.

*018.Complete Chart B for neutral atoms.

Chart A

Kind of Atomic Mass Number of Number of Number of

Atom Number Number Isotope Protons Electrons Neutrons

________ ________ ________^2110 Ne ___________ ___________ ___________

chlorine ________ 35 _______ ___________ ___________ ___________

________ 28 58 _______ ___________ ___________ ___________

________ ________ 40 _______ 18 ___________ ___________

Chart B

Kind of Atomic Mass Number of Number of Number of

Atom Number Number Isotope Protons Electrons Neutrons

selenium ________ ________ _______ ___________ ___________ 40

________ ________ ________^1105 B ___________ ___________ ___________

________ ________ ________ _______ ___________ 35 46

________ ________ 104 _______ ___________ 45 ___________